‘Sonet’ is an open pollinated hybrid of an unpatented Citrus unshiu variety ‘Miho Wase’ (unpatented) (the female seed parent). In 1996 open pollinated fruit was collected from ‘Miho Wase’ trees adjacent to Citrus reticulata varieties ‘Nova tangelo’ (unpatented), ‘Ellendale’ (unpatented) and ‘Novelty’ (unpatented) (possible male pollen parents). The seeds from each fruit were extracted and planted. Zygotic seedlings were selected in the nursery in 1997, by leaf morphology. The 14 selected seedlings were budded to ‘Troyer citrange’ (unpatented) rootstocks and planted on a trellising and arching system in a forcing house, in 1998, situated in Addo, in the Eastern Cape province of the Republic of South Africa (global positioning satellite co-ordinates 25° 42′E.; 33° 34′S.). Due to the early maturing and fruiting of citrus trees grown on the trellising and arching system, the first fruit was set in 2000. These trees were then evaluated for fruit quality traits. Based on the results of this evaluation, one of the aforementioned trees was selected for further evaluation, resulting in the present ‘Sonet’ variety. ‘Sonet’ was made subject of a South African Plant Breeders' Rights application on 5 Dec. 2006. This application was subsequently granted in 2009 under number ZA 20094289.
The time of fruit maturity (early to mid April), makes this selection an early maturing variety. Good flavour (mandarin-like) and firm fruit with a good shelf life of at least four weeks from maturity make ‘Sonet’ superior to the ‘Satsuma’ (unpatented) and early ‘Clementine’ (unpatented) in the market at this time.
Trees bear a good to excellent crop from the fourth year after planting. Alternate-bearing has not been noted. There is a small percentage of splitting in February and as with all early maturing mandarin cultivars, some fruit are lost to sunburn.
‘Sonet’ was first asexually propagated in Addo, South Africa in 2000 when buds were collected from a hybrid seedling designated WH/B/02/36 (1740). Three trees were topworked onto ‘Carrizo citrange’ (unpatented) rootstocks and one tree onto a ‘Rosehaugh’ (unpatented) mandarin rootstock. These four trees of ‘Sonet’ were initially used for evaluation and description purposes. Two more trees were top worked onto ‘F80/9 citrumelo’ (unpatented) rootstocks in 2001 for evaluation purposes. In 2005 three budded nursery trees were planted out on ‘Troyer citrange’ rootstocks for evaluation. The first trialorchard of ‘Sonet’ was planted at Addo in February 2006. This consisted of budded nursery trees, 125 trees on ‘Carrizo citrange’ rootstock and 19 trees on ‘Troyer citrange’ rootstock. In 2009 a further 24 budded nursery trees on C35 rootstock and four trees on ‘Carrizo citrange’ rootstock were planted for evaluation. All characteristics of the original tree and its fruit as determined and described appear to be transmitted through succeeding asexual propagations. No incompatibility or other rootstock related problems have yet been observed. The mother tree is still growing in the forcing house on the trellising and arching system in a 20 liter pot, as of 2012, 14 years old. The tree is in a fair condition and is still bearing good quality fruit.
Further, ‘Sonet’ has been cleansed of all graft transmissible viruses and viroids by shoot-tip grafting (STG), followed by pre-immunization with a light strain of the Citrus tristeza virus (LMS6). This was done through a regulated process, which involves taking vegetative buds from the mother tree and introducing the same into the South African Citrus Improvement Scheme. In this process, plant material is shoot-tip grafted to provide a virus-free source of bud wood material. Material so obtained is then pre-immunized with a mild strain of the aforementioned Citrus tristeza virus, followed by a certification by the relevant South African citrus authority. In addition, ‘Sonet’ is free from Apple Stem grooving virus (Capillovirus spp.), psorosis virus (Ophiovirus), Impietratura (Citrus impietratura agent (CSI000)), Citrus Viroids (CVD I: Genus Apscaviroid species: Citrus viroid CVd-I (CBLVd), CVD II: Genus Hostuviroid species: Citrus viroid CVd-II (HSVd), CVD III: Genus Apscaviroid species: Citrus viroid III (CVd-III), CVD IV: Genus Cocadviroid species: Citrus viroid IV (CVd-IV), CVD V: Genus Apscaviroid species: Citrus viroid V (CVd-V)), and Exocortis (Family Pospiviroidae, Genus Pospiviroid, species citrus exocortis viroid CEVd).
The present variety is distinguishable over ‘Miho Wase’ Satsuma (Citrus unshiu) which is as the closest variety to ‘Sonet’, in the following ways. ‘Sonet’ differs in leaf morphology from the ‘Miho Wase’, matures about two weeks later than the ‘Miho Wase’, has a smoother firmer and tighter rind, does not puff easily, and has improved flavour over ‘Miho Wase’. Fruit of ‘Sonet’ could contain some seed under cross pollination conditions, while fruit of ‘Miho Wase’ will be seedless under similar conditions. ‘Sonet’ matures earlier than any of its possible male pollen parents.